Graduate student Feichen Yang mixes two different hydrogel types to create a double-network hydrogel. One of the hydrogels is stiffer and stronger. The other hydrogel is softer and stretchier. By adjusting the relative amounts of the two hydrogel types, Yang can adjust the strength and elasticity of the 3D printed output to best match those characteristics in human cartilage. Yang published his work in ACS Biomaterials Science and Engineering and in Duke Today. Other hydrogel sources have been used to create cartilage replacements in the past, but because hydrogels are mostly water, previous attempts have tended to be unstable, not as strong as human tissue, and “runny.” By mixing hydrogels with different properties and adjusting the mix for specific applications, the double-hydrogel cartilage replacements can have greater integrity and be less likely to “leak.”

The promise of Yang’s research lies in the ability to take measurements from a specific patient’s MRI scans. Those images can form the patterns to 3D print replacement cartilage pieces for various parts of the body. Cartilage in various parts of the human body varies in length, strength, and elasticity and those factors, too, can be accounted for with a dual source mixture.